[Java知识库]JAVA synchronized 两个小案例

买票

package com.example.demo.hmjuc.day3;

import java.util.Random;
import java.util.Vector;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @author zhangqi
 * @date 2022/4/17 14:54
 */
public class Test1 {
    public static void main(String[] args) {
        while (true) {
            TicketWindow ticketWindow = new TicketWindow(2000);
            Vector<Thread> objects = new Vector<>();
            AtomicInteger atomicInteger = new AtomicInteger(0);

            for (int i = 0; i < 10; i++) {
                Thread thread = new Thread(() -> {
                    int count = new Random().nextInt(5) + 1;
                    // System.out.println("count = " + count);
                    int sale = ticketWindow.sale(count);
                    // System.out.println("sale = " + sale);
                    atomicInteger.addAndGet(sale);
                });
                thread.start();
                objects.add(thread);
            }
            objects.forEach(thread -> {
                try {
                    thread.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });

            int i = 2000 - atomicInteger.get();
            int ticket = ticketWindow.getTicket();
            if (i != ticket) {
                System.out.println(2000 - atomicInteger.get());
                System.out.println("ticketWindow.getTicket() = " + ticket);
                System.out.println("出现了线程安全问题 ");
                break;
            }
        }

    }


}

class TicketWindow {
    private int ticket;

    public int getTicket() {
        return ticket;
    }

    public void setTicket(int ticket) {
        this.ticket = ticket;
    }

    public TicketWindow(int ticket) {
        this.ticket = ticket;
    }

    public synchronized int sale(int num) {
        if (ticket >= num) {
            ticket -= num;
            return num;
        } else {
            return 0;
        }
    }
}

转账

package com.example.demo.hmjuc.day3;

import java.util.Random;

/**
 * @author zhangqi
 * @date 2022/4/17 15:20
 */
public class Test2 {
    public static void main(String[] args) throws InterruptedException {
        while (true) {
            Account account1 = new Account(1000);
            Account account2 = new Account(1000);
            Thread thread1 = new Thread(() -> {
                for (int i = 0; i < 100; i++) {
                    account1.transfer(account2, new Random().nextInt(100) + 1);
                }
            });
            Thread thread2 = new Thread(() -> {
                for (int i = 0; i < 100; i++) {
                    account2.transfer(account1, new Random().nextInt(100) + 1);
                }
            });
            thread1.start();
            thread2.start();
            thread1.join();
            thread2.join();
            int i = account1.getMoney() + account2.getMoney();
            System.out.println("i = " + i);
            if (i != 2000) {
                break;
            }
        }
    }

}

class Account {
    private int money;

    public Account(int money) {
        this.money = money;
    }

    public int getMoney() {
        return money;
    }

    // public synchronized void setMoney(int money) {
    //     this.money = money;
    // }
    //
    // public synchronized void transfer(Account target, int money) {
    //     if (this.money >= money) {
    //         this.setMoney(this.getMoney() - money);
    //         target.setMoney(target.getMoney() + money);
    //     }
    // }
    public void setMoney(int money) {
        this.money = money;
    }

    public void transfer(Account target, int money) {
        synchronized (Account.class) {
            if (this.money >= money) {
                this.setMoney(this.getMoney() - money);
                target.setMoney(target.getMoney() + money);
            }
        }
    }
}

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